1. Field of the Invention
This invention relates to the field of door latch apparatus, and in particular to a trim apparatus to be paired with a handle and mounted externally from the lock, the trim apparatus being adapted to the physical attributes of the particular handle, to cancel any variation in operational effects of the handle from a norm, for example, the cantilevered weight of the handle.
2. Description of the Prior Art
Closure mechanisms for doors are more and more frequently designed with lever handles rather than doorknobs to effect retraction of a bolt or the like. Handle mechanisms are usually cantilevered on a spindle, that is, a substantial portion of the weight of the lever handle is disposed asymmetrically around the axis of the spindle, whereby the force of gravity urges the spindle to rotate. The latch mechanism is normally spring-biased against rotation of the spindle, but with a very long or heavy handle, it may be necessary to somehow bias the lever handle to stay at a home position in order to prevent spontaneous opening of the latch mechanism.
Although use of a lever handle causes an uneven weight to be mounted on the spindle, such a lever handle is much easier for people to operate than the conventional doorknob in which the user-gripped portion of the latch is a smooth body having portions symmetrically distributed around the axis of the spindle. Lever handles are normally easier to grasp than knobs, and allow the user greater leverage on the spindle to cause retraction of the bolt mechanism and open the door. Lever handles are therefore preferable over knobs in many instances. In some instances, lever handles are a necessity, for example, closures adapted for use in areas where users may be expected to be frequently carrying loads, and public buildings and the like which must be fully accessible to handicapped persons.
Standards for lever handles for use by handicapped persons go beyond the simple requirement of a cantilevered lever portion. A handle contour in the shape of a "C" is required according to some standards such that the greater part of the body of the lever handle is spaced (e.g., 2 in. or 5.0 cm.) from the door, and the extreme end of the lever handle will be disposed within a minimum distance (e.g., 0.5 in. or 1.3 cm.) of the surface of the door. The additional weight due to the segment spacing the end of the lever handle within the minimum distance required by the standards, results in a substantial additional weight placed well away from the turning axis of the device, that is, the spindle. Of course, a relatively smaller weight placed at a greater distance from the axis will have the same rotational force, or "moment arm," as a relatively larger weight placed closer to the axis.
Use of a lever handle on a latch mechanism in which the spindle is rotatable in either direction is difficult because of the uneven load of the lever handle. It has been known in the art to bias cantilevered lever handles against the force of gravity by use of a positive stop defining a "home" position of the latch mechanism, the stop restricting spindle rotation to one direction. U.S. Pat. No. 2,470,771--Harvey discloses a lever handle and bolt retraction mechanism in which a coil spring wrapped around a hub attached to the spindle, within a mortise lock, biases the spindle against angular displacement from a home position. An additional coil spring mounted on a shaft carrying the retractable bolt also urges the hub and spindle to rotate opposite the bolt retraction direction. In other words, the bolt spring biases the lever handle upwards against the force of gravity, an extension of a hub mounted to the spindle being resiliently urged against an immovable abutment within the latch mechanism.
According to devices such as that of Harvey, it is known in the art to oppose the weight of a lever handle by biasing the handle upwardly against a stop. The rest position of the lever handle may therefore be set at precisely horizontal, for optimum accessibility and neat appearance. No sagging of the handle position is expected because handle position does not relate to a balancing of springs which will wear and sag. During wear of the biasing springs in even a positively stopped latch, however, a lever handle which is inadequately biased upwards will tend to sag, leaving play in the lock and possibly causing spontaneous opening of the door. A lever handle which is disposed at all below horizontal in its rest position is noticeably sloppy in appearance. Therefore, it is conventional practice in the prior art to strongly bias the lever handle upwards.
According to prior art devices having a given biasing spring associated with a part of the latch mechanism for upwardly biasing the position of the lever handle, regardless of the handle or knob mounted on the spindle in a particular installation, the full upward force defined by the biasing spring remains. This bias is determined by the latch mechanism and is not variable as required for a certain handle. Therefore, the user of any latch mechanism was necessarily required to exert sufficient force to overcome the biasing built in for the worst case situation, that is, for a heavy cantilevered lever handle mechanism.
The present invention takes a different view of the use of lever handles, knobs and the like. According to the invention, the latch mechanism is provided with the minimum, rather than the maximum, force necessary to maintain the home position of the spindle. In other words, the internal portion of the latch mechanism is adapted for reliable operation with the lightest of possible handles, rather than the heaviest. External trim fittings which are matched to the particular desired handle, offset the weight of the handle. Accordingly, it is possible to provide a nearly balanced, easily operated latch mechanism and a more or less biased external trim plate, as needed to balance the physical attributes of the particular knob or handle.
The variable bias trim mechanism according to the invention is accomplished using a movable "home" position defined by springs in the trim. The mechanism is useful not only for accommodating various handle mechanisms and various moment arms, but also for accommodating opposite handle mountings in which the direction of the spring bias must be reversed. According to the invention, one need only move the adjustable portion of the trim plate that defines the bias spring home position from one side of center to the other, in order to change the trim bias from clockwise to counter-clockwise. Accordingly, the trim is equally operable to bias lever handles on both sides of the door, a lever handle on one side and knob on the other, or as may otherwise be required for a range of handle members.
U.S. Pat. No. 2,729,485--Schlage shows a coil spring disposed in the trim on the surface of a door, the coil spring being adapted to maintain a lever handle at a home position. Heavier springs are recommended in connection with heavier lever handles, and the heavier springs are mounted in trim mechanisms associated especially with such handles. The device relates spring tension to the lever handle, but even given the foregoing description, Schlage fails to employ a movable home position, whereby installation is facilitated and the device is equally applicable to either side of the door. Instead, Schlage uses the device with a spindle which is rotatable in either direction to withdraw the bolt. Accordingly, with wear on the springs, the Schlage device will be expected to sag, the unequal load caused by the cantilevered lever handle eventually altering the single spring's rest position or placing unequal stress on two opposed springs. The Schlage device is apparently designed to maintain symmetrical force around at least one immovable centering tab. Therefore, even if the symmetrical nature of the device was somehow defeated, the user would be required to manually oppose the bias in order to mount the respective parts, because of the immovable nature of the centering tab.
According to the present invention, not only a heavier spring, but also a movable home position may be associated with the trim mounted on the surface of the door. Users need not therefore overcome worst-case biasing forces in order to use various operators, including lever handles. Installers need not overcome biasing at all in order to align the trim for correct installation.